Drilling rigs are complex installations that include the equipment needed to drill various types of wells such as water wells, oil wells, or natural gas extraction wells. As is well known, drilling rigs can be mobile or more permanent land or marine-based structures that incorporate many different pieces of equipment. Generally, modern land-based drilling rigs are smaller and more mobile in order to address the increasing need for frequent relocation to new drilling sites.
In the oil and gas industry, drilling rigs have various speed and power requirements for different stages of the drilling process namely during downhole movement when a drill string is being lowered or pushed to the drilling face, during drilling itself and during tripping when the drill string is being lifted to surface.
The equipment used on the drilling rig for raising and lowering a drill string and for conducting drilling has evolved over the years. A conventional “draw-works” is the primary machinery used to hoist and to lower the drill string of a drilling rig. The main function of a draw-works is to provide a means of raising and lowering the traveling blocks of the drilling rig. A conventional draw-works consists of five main parts: the drum, the motor(s), the reduction gear, the brake, and the auxiliary brake. The motors can be AC or DC-motors, or the draw-works may be connected directly to diesel engines using metal chain-like belts. This arrangement can provide a number of gears for hoisting and lowering a drill string, which can be selected according to the various power requirements of different stages of operation of a drilling rig.
The equipment costs, fuel costs and relatively large physical footprints of conventional draw-works and various operational limitations have provided the incentive to re-engineer conventional drilling rigs. This effort is of particular importance for small mobile drilling rigs where the need to reduce the physical footprint of a rig is required to enable access and/or operation at particular sites.
Stage III rigs use hydraulic cylinder hoisting systems to raise and lower the drill string. While such systems are generally more compact and, hence mobile, they are generally not as versatile for deep drilling because of the increased hook-loads associated with deep drilling. That is, as well depth increases, the power requirements of hydraulic cylinder hoisting systems increases significantly from the need for more pumps, larger hydraulic fluid reservoirs and additional costly modifications to related equipment.
As is well known, a hydraulic cylinder is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. Hydraulic cylinders have many applications, notably in construction equipment (engineering vehicles), manufacturing machinery, and civil engineering. Such hydraulic cylinders typically provide an enclosure having a piston and piston rod slidably disposed within the enclosure, wherein the piston rod extends outwardly from the cylinder. Pneumatic or hydraulic passageways are provided at each end of the cylinder, whereby pressurized fluid is supplied or exhausted on either side of the piston, thereby forcing the piston and piston rod to move from one end of the cylinder to the other. The piston and the piston rod move simultaneously to provide linear actuator movement to an object. Through such movement, an actuation force is imparted on the object as the piston rod moves between an extended position, wherein the piston rod extends outward from the cylinder, and a retracted position, wherein the piston is drawn into the cylinder.
It is often desirable, however, to have variable actuation forces applied to the object as the piston rod moves between the first position and the second position. Previous designs have attempted to vary the actuation forces applied to the object by manipulating the pressure levels within the power cylinder.
For example, U.S. Pat. No. 3,969,712 to Sung describes a three section telescopic cylinder ram for use in applications such as operation of multi-section telescopic crane booms. The ram has the ability to have its mid-section and interior or rod section independently actuated. The mid-section and rod section of the ram may be extended or retracted as a unit relative to the exterior base section, or the mid-section and rod section may move relative to each other in either direction while moving relative to the base section.
US Patent Application No. 2006/0169132 to Tucker describes a linear hydraulic actuator of the kind that includes a hydraulic piston and cylinder arrangement, the piston of which can be moved in extend and retract directions relative to the cylinder by application of hydraulic fluid under pressure to the piston within the cylinder. An exemplary application is in actuation of a thrust reverser system in an aircraft gas turbine engine where the cowl or other movable component is moved between deployed and stowed positions by a linear hydraulic actuator.
U.S. Pat. No. 6,895,854 to Plattner describes a power cylinder apparatus for supplying varying actuation forces to a workpiece through the supply of a constant fluid pressure. This reference teaches that different actuation forces are imparted on the workpiece as a result of fluid pressure on different surface areas of components of the cylinder.
U.S. Pat. No. 4,011,724 to Landes et al. describes an actuator for selectively and sequentially providing dual pressure forces for positioning and seating fasteners and for other purposes. The actuator is caused to be extended a first distance at low force and then to be extended an additional distance at a relatively higher force. Air pressure is selectively applied to cause all pistons and the actuating rod to retract to their initial positions.
U.S. Pat. No. 3,904,416 to Onoda et al. describes a multistage cylinder comprising at least a first-stage cylinder and a second-stage cylinder provided essentially in the piston rod of the first-stage cylinder. The first-stage and second-stage cylinders are capable of operating separately and independently of each other and are also capable of operating in opposite directions. Application of the device to industrial robots is described.
U.S. Pat. No. 5,186,095 to Todd describes a piston assembly comprising a piston cylinder including a velocity tube which extends through the piston head. Hydraulic controls are connected to the cylinder and to hydraulic lines for operating purposes. In use, fluid under pressure is directed into the velocity tube which communicates with the hollow piston rod conduit, forcing the piston along its downward stroke while prefilling the piston well with fluid. Once the work load is met, additional power is supplied to the piston as fluid is pumped into the cylinder above the piston head to apply additional hydraulic pressure for the force necessary for the work load encountered. These dual power stages cause the piston assembly to function efficiently since only a small amount of power or force is required to drive the piston during its initial stage, to bring it into contact with the work load. Thereafter, the second stage or hydraulic force provides the additional power needed to perform the work on the particular load.
U.S. Pat. No. 4,955,282 to Ranson describes a multi-chamberal hydraulic cylinder and valve system which utilizes a single relatively low flow rate pump to provide pressurized fluid during travel, compression and retraction of the piston rod. In the system, the pressurized fluid flow rate is uniform throughout the cycle of operation of a hydraulic ram which can be extended over a large low force stroke.
U.S. Pat. No. 6,890,406 to Aho describes a three-chamber cylinder that uses two rod end chambers and a large middle blind chamber. The two rods are moved simultaneously in and out from the middle blind chamber. The rods are moved at a set rate to tighten or slack off of the roll mantle, the pressures in the three chambers are kept at a constant to hold the system in a set position. The three chambers in the multi-displacement cylinder are used to push a single rod at varying speeds and pushing capabilities by varying the flow of oil to each of the three chambers. This allows the cylinder to handle large loads at slower speeds. The speed can be increased with a concomitant lowering of the load handling capacity of the cylinder.
U.S. Pat. No. 5,191,828 to McCreery describes a telescopic cylinder that is guided along a larger piston sleeve throughout the stroke of the entire cylinder. The cylinder sections telescopically extend through the more rigid tubular section allowing for larger loads to be moved. The cylinder can hoist larger loads a set distance without using a telescopic cylinder to meet the hoisting distance needs.
U.S. Pat. No. 6,029,559 to Barthalow and Zimmerman describes a system of multiple telescopic cylinders that can be controlled independently to raise and lower different sections of a boom. The cylinder system described uses multiple cylinders to extend and retract different sections of a telescoping system; the system allows for the control of each telescopic section independently of the others.
U.S. Pat. No. 6,293,359 to Dobran et al. describes a drilling apparatus that uses a cylinder to push down on a drill bit for drilling holes for blast hole drilling. The cylinder is used to move the drill bit to a rock face. A feed force is applied to the drill bit at the rock face and a reducing feed force is used to withdraw the drill bit from the hole. The cylinder has two sides to force the cylinder to move up and down due to differential pressure between the pull down and hold back sides of the cylinder.
U.S. Pat. No. 2,502,895 to Shaffer describes a hydraulic hoisting system for a drilling rig. The system includes three cylinders, two of which are configured with piston rods (connected to a cross head which supports the central third cylinder). The piston rod of the third cylinder has a hook attached thereto, for making a connection to a drill string. Switching of pressurized hydraulic fluid to direct it into various hydraulic lines can induce raising or lowering of the cross head independently of the central cylinder.